The present invention relates to a scanning electron microscope for inspecting and measuring a sample by scanning an electron beam to the sample, particularly to a method and a scanning electron microscope for inspecting and measuring a sample by scanning an electron beam to a sample, charging the sample, and scanning another electron beam to the sample under a charged state.
In recent years, in the light of high integration and micronization of a semiconductor element, a variety of patterns are formed on a sample (a semiconductor wafer, for example), and evaluation and measurement of their shape and size are becoming important more and more.
Particularly, in a contact hole for obtaining electric conduction between layers in multilayering, the diameter of the hole is becoming minute as micronization proceeds, and a contact hole with an aspect ratio (depth of contact hole/diameter of hole) of over 30 is not uncommon at present.
To observe and measure this contact hole, it is necessary to detect a secondary electron excited by a primary electron beam (hereinafter referred to also as electron beam), however, as the aspect ratio becomes larger, the possibility that the secondary electron collides the side wall of the hole and disappears in the hole becomes high, and as a result, there is a problem that observation and measurement of the bottom of the hole become difficult. To solve this problem, the secondary electron generated at the bottom of the hole is required to be taken out to outside of the contact hole at least.
To realize this, there is a technology (hereafter referred to also as pre-dose) that, by performing preliminary irradiation of a primary electron beam prior to electron beam scanning for inspection and measurement (hereinafter referred to also merely as observation), the region for inspection and measurement is made charge positively thereby taking out of the electron from the contact hole is facilitated.
In the patent document 1, a technology is described wherein, prior to electron beam scanning for observation, an electron beam is irradiated to wider area than that by the magnification of the time of observation (that is, by a lower magnification than that for observation) including the observation region, thereby pre-dose is realized.
Also, in the patent document 2, a technology is described wherein, prior to electron beam scanning for observation, a sample is subjected to preliminary irradiation of an electron beam whose secondary electron emission efficiency δ is larger than 1.0, the surface of the sample is charged positively, thereafter an electron beam whose secondary electron emission efficiency δ is nearer to 1.0 compared with the electron beam used for the preliminary irradiation is scanned, thereby sample observation is performed while maintaining the positively charged state stably.
Further, the patent document 3 describes that, in the relation between the magnification in preliminary irradiation and the positive charge voltage, the larger the area of preliminary irradiation, the higher the positive charge voltage which is formed on the sample.
Also, in the patent document 4, a method is described wherein, an electron emission means called flat gun, other than an electron optical system for observation and measurement, is additionally provided within the microscopy body of an electron microscope and charge is formed by overall irradiation by a large electric current.    (Patent Document 1) Japanese Published Unexamined Patent Application No. H5-151927 (corresponding to the U.S. Pat. No. 5,412,209)    (Patent Document 2) Japanese Published Unexamined Patent Application No. 2000-200579 (corresponding to the U.S. Pat. No. 6,635,873)    (Patent Document 3) WO03/007330 (corresponding to the U.S. Pat. No. 6,946,656)    (Patent Document 4) Japanese Published Unexamined Patent Application No. 2000-208579 (corresponding to the U.S. Pat. No. 6,232,787)